The invention relates to control systems for disconnect or start switches for use with the start or auxiliary winding of a single phase AC induction motor. The invention particularly relates to continuing development efforts regarding the circuitry shown in commonly owned co-pending allowed U.S. application Ser. No. 680,489, filed Dec. 11, 1984, "Load And Speed Sensitive Motor Control Starting Circuit", Shemanske et al, hereby incorporated herein by reference.
A single phase AC induction motor has a main winding for running the motor, and a start or auxiliary winding for starting the motor. The auxiliary winding is energized when starting the motor from rest and then disconnected at a given motor speed. The fields in the main and auxiliary windings are phase shifted, for example by capacitance, inductance, resistance or the like, to establish a rotating magnetic field for starting and/or running torque. The circuitry of the present invention is useful for capacitor start/run motors, and also for capacitor start only motors, especially those of higher rating, e.g., greater than 2 horsepower.
The present invention addresses a potential problem when restarting the motor from a coasting or running condition. For example, during a momentary power outage, the motor is de-energized but continues to rotate, i.e., coast, particularly in high inertial load applications. If electrical power is then re-applied to both the main winding and the start winding and start capacitor and/or run capacitor, an over-current condition may occur, damaging the capacitor and/or start switch in particular. If electrical power is re-applied to the auxiliary winding and start capacitor during this coasting condition, excessive current may flow through the capacitor and through the start switch. Burned out start and/or run capacitors and start switches may result from temporary power outages.
The present invention addresses and solves the above noted problem, and protects against an over-current condition if the motor is de-energized while in the running mode and then re-energized while still coasting above a given speed.